TF Advanced Derived Column Transfrom: check result of an expression against data type
If you have an expression like this: iif(LOEVM = "X" or LOEVM = "1", "1", "0") and a Data Type DT_BOOL then the result at the test input will always show 1 or 0.
In reality the expression will always result in 0, because there is a conversion from a string to a boolean content.
So the correct expression would be iif(LOEVM = "X" or LOEVM = "1", 1, 0). The problem is, that it always looks like a working expression within the expression editor.